feat: Disable Watchdogs when USB-Serial-JTAG is used

Watchdog needs to be disabled in order to preven reset in the middle of
a communication. By default watchdog is disabled after chip reset,
but second stage bootloader may enable it again and if application does
not disable it, it will reset the device, because USB-Serial/JTAG does
only software reset.

Author: Dzarda7

include/esp-stub-lib/usb_serial_jtag.h

@@ -16,6 +16,15 @@ extern "C"
 
 #define USB_SERIAL_JTAG_OUT_RECV_PKT_INT_ENA    (0x1 << 2)
 
+/**
+ * @brief Disable watchdogs for USB-Serial/JTAG
+ *
+ * This function disables the watchdogs for USB-Serial/JTAG to prevent the device from resetting.
+ * By default watchdog is disabled after chip reset, but second stage bootloader may enable it again,
+ * and if application does not disable it, it will reset the device, because USB-Serial/JTAG does only software reset.
+ */
+void stub_lib_usb_serial_jtag_disable_watchdogs(void);
+
 /**
  * @brief Check if USB-Serial/JTAG is currently being used for communication
  *

src/target/base/include/target/usb_serial_jtag.h

@@ -9,6 +9,15 @@
 #include <stdint.h>
 #include <stdbool.h>
 
+/**
+ * @brief Disable watchdogs for USB-Serial/JTAG
+ *
+ * This function disables the watchdogs for USB-Serial/JTAG to prevent the device from resetting.
+ * By default watchdog is disabled after chip reset, but second stage bootloader may enable it again,
+ * and if application does not disable it, it will reset the device, because USB-Serial/JTAG does only software reset.
+ */
+void stub_target_usb_serial_jtag_disable_watchdogs(void);
+
 /**
  * @brief Attach interrupt handler to USB-Serial/JTAG and configure interrupts
  *

src/target/esp32c3/src/usb_serial_jtag.c

@@ -10,13 +10,30 @@
 #include <target/usb_serial_jtag.h>
 #include <soc/usb_serial_jtag_reg.h>
 #include <soc/interrupt_core0_reg.h>
+#include <soc/rtc_cntl_reg.h>
 #include <soc_utils.h>
 
 // External ROM functions
 extern void esp_rom_isr_attach(int int_num, void *handler, void *arg);
 extern void esp_rom_isr_unmask(int int_num);
 extern void esprv_intc_int_set_priority(int int_num, int priority);
 
+#define RTC_CNTL_WDT_KEY 0x50D83AA1
+#define RTC_CNTL_SWD_KEY 0x8F1D312A
+
+void stub_target_usb_serial_jtag_disable_watchdogs(void)
+{
+    // Disable RWDT (RTC Watchdog)
+    WRITE_PERI_REG(RTC_CNTL_WDTWPROTECT_REG, RTC_CNTL_WDT_WKEY);
+    WRITE_PERI_REG(RTC_CNTL_WDTCONFIG0_REG, 0x0);
+    WRITE_PERI_REG(RTC_CNTL_WDTWPROTECT_REG, 0x0);
+
+    // Configure SWD (Super Watchdog) to autofeed
+    WRITE_PERI_REG(RTC_CNTL_SWD_WPROTECT_REG, RTC_CNTL_SWD_WKEY);
+    SET_PERI_REG_MASK(RTC_CNTL_SWD_CONF_REG, RTC_CNTL_SWD_AUTO_FEED_EN);
+    WRITE_PERI_REG(RTC_CNTL_SWD_WPROTECT_REG, 0x0);
+}
+
 void stub_target_usb_serial_jtag_rominit_intr_attach(int intr_num, void *handler, uint32_t flags)
 {
     // Route USB interrupt to CPU